1. Field of the Invention
This invention relates to an intelligent power device module that has a power device chip and a control device chip for controlling the power device chip put on a single mounting board substrate.
2. Description of the Related Art
In this specification, a semiconductor device module that has a power device chip and a control device chip put on a single mounting board is called an intelligent power device module.
A mounting board used for intelligent power device module is such that wiring (conducting) patterns are formed on an insulating layer of epoxy resin which is formed on a metal base of aluminum. FIG. 1A is a plan view of a conventional intelligent power device module; FIG. 1B is a sectional view taken along line 1B--1B of FIG. 1A; and FIG. 2 is a view showing the capacitances parasitic on the intelligent power device module of FIGS. 1A and 1B.
As shown in FIGS. 1A and 1B, for example, on a metal base 1 of aluminum (Al) is formed an insulating layer 22 of an epoxy-resin thin film, onto which a wiring patterns 3 are attached to complete the mounting board. For example, a power semiconductor device 4 mounted on a heat spreader 9 of copper (Cu), a control circuit device 5, and other elements are put on the mounting board with bonding wires 8 electrically connecting the semiconductor elements including the power semiconductor device chip 4 and control circuit device chip 5 to the wiring patterns 3. The heat spreader 9 is an indispensable part in mounting an element that generates a lot of heat, such as the power semiconductor device 4. In semiconductor power device modules, since the power semiconductor device 4 produces a large amount of heat, the metal base 1 is attached to a heat sink (not shown) before use. To improve the heat-dissipating characteristics of the power semiconductor device, it is desirable that the thickness of the insulating layer 22 of epoxy resin should be as thin as possible. However, to achieve a breakdown voltage of 3 kV to 5 kV which is generally required, the thickness of the insulating layer must be several tens to hundred micrometers. In a semiconductor power device module with such an arrangement, parasitic capacitances C1 and C2 are formed via the insulating layer between the wiring patterns 3 and the metal base 1 as shown in FIG. 2. Because such a capacitance is formed between every block of the wiring patterns 3 and the metal base 1, the capacitances of any two pattern blocks are connected in series. As a result, a capacitive coupling takes place between the power semiconductor device chip 4 and the control circuit device chip 5.
With the large coupling capacitance, when the power semiconductor device chip 4 is caused to switch a high voltage at a high speed, which creates a high dV/dt state, the control circuit will malfunction. The capacitance (C) formed is determined by the wiring pattern area (S), the insulating layer's permittivity (.epsilon.), and the insulating layer's thickness (d), and is expressed as C=.epsilon..times.S/d. In the conventional module, because the permittivity (.epsilon.) of the insulating layer of epoxy resin is not low, and the insulating layer's thickness (d) is thin for heat dissipation of the power semiconductor device, the capacitance formed is relatively large. With a semiconductor of such a construction, therefore, an attempt to switch a high voltage at a high speed permits abrupt changes in the voltage at the power semiconductor device chip 4 to cause differential voltages on the control circuit pattern because the coupling capacitance between the power semiconductor device chip 4 and the control circuit device chip 5. This can cause the control circuit to malfunction.